In engines configured with port injection, during the engine start as well as the engine warm-up period, the presence of a cold intake valve can result in poor fuel vaporization. This can cause poor tailpipe emissions, engine hesitations, and poor engine start robustness. The issues may be exacerbated in hybrid vehicles where the engine remains shutdown for prolonged periods of time. To compensate for the emissions, expensive emissions control systems may be required, such as catalysts including increased levels of precious metals, or even specialized systems that enable the exhaust catalyst to be electrically heated. Still other approaches that include heavy spark retard usage or increased fuel injection result in wasted fuel economy.
The inventors herein have recognized that fuel vaporization and resulting tailpipe emissions are highly sensitive to intake valve temperature. In particular, the fuel injector sprays into the intake manifold near the back-side of the intake valve. Then when the intake valve opens, the fuel passes over the intake valve as the fuel is sucked into the chamber. This proximity makes the intake valve temperature influence the fuel vaporization and resulting emissions. As such, since the intake valve is in direct contact with the fuel, and because it is low mass, it can heat up faster than the engine combustion chamber walls or the intake manifold.
Internal combustion engines may also be configured with a laser system that includes a laser ignition device coupled to each engine cylinder. The laser system may be used for various approaches, such as to initiate cylinder fuel combustion and controlling a pilot injection by changing the energy level of a laser pulse directed into the engine. As another example, a photodetector of the laser ignition system may be used for determining the position of a piston inside the cylinder. The inventors herein have recognized that laser ignition systems can be leveraged to expedite intake valve heating. In particular, a laser beam can be used to sweep the intake valve surface and increase the intake valve temperature. In one example, emissions related to poor fuel vaporization, particularly in port injected engines, may be reduced by a method for an engine, comprising: operating a laser ignition device with an output that is adjusted from (for example to be lower than) a level for initiating cylinder ignition, the output adjusted based on intake valve temperature.
As one example, prior to an engine start, such as when a vehicle is unlocked by the operator, an intake valve temperature may be estimated and/or inferred based on the output of one or more engine sensors. A target valve temperature is then determined based on ambient conditions such as ambient temperature, barometric pressure, as well as fuel conditions including octane content of fuel available in the fuel tank. A laser ignition device of the engine may then be operated at a lower power level (than the power level required to initiate cylinder ignition), even before an engine start is requested, to expedite valve warming. The output of the laser device, including a pulse frequency of the laser beam, may be adjusted based on a difference between the estimated valve temperature and the target valve temperature. For example, the power level for valve heating may be reduced from the power level for cylinder ignition at a degree based on the difference between the estimated valve temperature and the target valve temperature. This allows the laser output to sufficiently heat the valve without damaging it. In addition, a target of the laser beam may be adjusted to perform a planar sweep of the intake valve. The engine may then be started, with cylinder fuel injection being resumed, after a threshold rise in intake valve temperature has occurred. Once the engine is started, the laser is continued to be operated in the lower power level during a cylinder intake stroke until the target valve temperature is attained. In one example, the controller may choose to delay the first engine start if the benefit of heating the valve exceeds the benefit of immediately starting the engine, such as in a hybrid vehicle where the vehicle may be propelled by the electric motor while the valve is warming up. For example, the beam trajectory may be adjusted so that the beam sweeps across the bottom of the intake valve when the valve is closed at the beginning of an intake stroke, and then follows the portion of the top of the intake valve that is within line of sight of the laser during the course of the intake stroke. During some conditions, such as very cold ambient conditions where the laser may not have enough time or energy to heat the entire intake valve before the engine start, the laser beam may be used to heat a smaller area of the intake valve to create a hot-spot. As such, after the engine has been started, the laser operation for heating the intake valve is performed in addition to laser operation at a higher power level during a compression stroke to enable cylinder combustion. Once the target valve temperature is reached, the lower power laser operation for valve heating may be disabled. The valve temperature may then continue to be monitored during engine operation, and laser operation in the lower power mode for valve heating may be resumed if the valve temperature drops, such as during a prolonged DFSO condition.
In this way, cylinder intake valves may be warmed by using existing engine components, such as an existing laser ignition system, without adding costs. By warming up the intake valve during or prior to starting an engine, fuel vaporization may be enhanced, improving engine start performance, particularly in engines fueled via port injection. In addition, warming up of the intake valve may reduce engine cold-start emissions. By maintaining the intake valve warm even during DFSO conditions, or during prolonged hybrid vehicle operation in an electric mode, engine hesitations are reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.